Scientists Shed Light On Snake River Salmon’s ‘Silent Killer’

4/2/2002 -- Portland, Ore. -- A study published recently by state and federal agency, university and private scientists concludes that juvenile Snake River salmon and steelhead die from delayed effects after passing as many as eight federal dams on their way to the Pacific, and that they do so at much higher rates than downriver stocks, which pass fewer dams. The federal government (in its 2000 Biological Opinion) acknowledged that such evidence linking “delayed mortality” to migration through the Columbia-Snake hydrosystem would build a much stronger case for removal of the four lower Snake River dams. Tomorrow, April 3, marks the official start to the spring migration season in the Columbia-Snake basin.

In the study’s conclusion, the authors state:

“This evaluation has implications for the analyses of management options for the recovery of Snake River salmon and steelhead. In those analyses, dam breaching appears to increase the survival of Snake River chinook salmon and may perhaps lead to eventual recovery of these stocks if delayed mortality is related to the hydrosystem experience . . . Given the evidence discussed here, we find significant support for the hypothesis that Snake River fish are subject to delayed mortality and that this effect is related to the hydrosystem.”

Published in a peer-reviewed journal of the American Fisheries Society, the study stands also as a major indictment of the elaborate and expensive programs – such as barging or trucking young fish around dams - that over decades have continued to fail to offset the dams’ lethal effects. It summarizes the considerable body of scientific research that shows how the various stresses associated with passing dams – either in-river or transported in barges and trucks – often inflict fatal harm to young fish, and that such harm compounds with the number of dams the fish must negotiate.

“This ‘delayed mortality’ from passing dams is the salmon equivalent of death from cigarettes,” said Jeff Curtis of Trout Unlimited. “It’s not the first pack of smokes that kills you; it’s the cumulative effects that kill you later on, and the more you smoke the better your chances are of that happening. The evidence in this study shows that for Snake River fish, those eight dams might as well be eight packs a day, and all the filters and low-tar gimmicks aren’t going to save them.”

Importantly, the study concludes that delayed mortality effects increased concurrently with the completion of the lower Snake dams in the 1960s and ‘70s, and that at the same time Snake River stocks declined more sharply than those originating down-river in the Columbia. Further, those declines continued despite the transportation programs along with changes in harvest levels and hatchery practices. With most habitat degradation of Snake River spawning and rearing habitat occurring before the salmon stocks nose-dived, as the study points out, the hydrosystem is left as the leading culprit.

“Whether you require a smoking gun, a process of elimination or both, there’s no shortage of evidence for what’s been killing Snake River fish, and all paths lead back to the dams,” said Nicole Cordan of Save Our Wild Salmon. “That familiar flag of uncertainty that opponents of dam removal like to wave as an excuse for inaction just won’t fly any more.”

The 2000 Biological Opinion on the Columbia River hydrosystem (which includes the lower Snake dams as well as the various mitigation programs) remains as the major decision document for dam-related fisheries management on the Columbia and Snake rivers. The first of three major decision points contained in the Biological Opinion is due next year.

With regard to delayed mortality and the four lower Snake dams, the BiOp states flatly that if lower Snake dam removal lowered delayed mortality as the study strongly indicates it would, then that action alone could recover four ESA-listed Snake River salmon and steelhead stocks (p. 9-278). Salmon advocates have long argued for a more comprehensive recovery plan that includes lower Snake dam removal.

”The issue of delayed mortality needs to be squarely addressed in the 2003 check-in on the Biological Opinion,” said Rob Masonis of American Rivers. “There has been too much focus on minor survival improvements at the dams, but the real issue is the cumulative mortality inflicted by the hydrosystem on the fish, and that issue should be front and center.”

The study, “Evidence Linking Delayed Mortality of Snake River Salmon to Their Earlier Hydrosystem Experience,” was authored by Phaedra Budy, Gary P. Thiede, Nick Bouwes, C. E. Petrosky and Howard Shaller. It was published in the North American Journal of Fisheries Management. An abstract of the paper can be viewed at www.fisheries.org in the “publications” section, and reprints of the full paper can be obtained through the American Fisheries Society by calling 301.897.8616 or by e-mailing journals@fisheries.org.